Recently, on the basis of the societal demand of resource-saving and energy-saving, a request for a lower fuel consumption of automobiles is growing gradually, and a tire which is excellent in wear resistance, crack growth resistance, etc. is in demand. It is known as a technique for improving the durability of the tire to stereoregularly control the micro structure of rubber components compounded to the tire.
On the other hand, it is known that natural rubber has a micro structure where the cis-1,4 bonding amount is 99.7%, and it is recognized that the strain-induced crystallizability is improved due to the high stereoregularity. Regarding the rubber composition using the natural rubber, it is capable of exhibiting high durability when used for a tire. Moreover, it is known that it is also possible to improve the durability by stereoregularly controlling the micro structure of polybutadiene.
It is disclosed in PTL1 that it is possible to synthesize a polybutadiene with a high cis-1,4 bonding amount by using a catalyst system obtained by adding conjugated diene monomer to neodymium compounds.
Moreover, disclosed in PTL2 is a technique for preparing a modified conjugated diene polymer having a modification efficiency of a specific value or more and a high cis-1,4 content in the conjugated diene moiety, by modification of a polymer with a specific modifier, the polymer being prepared by polymerization of a conjugated diene compound using a catalyst containing a lanthanoid rare earth metal compound in an organic solvent and having an active organic metal site, the modified conjugated diene polymer.